U.S. officials say a recent attack on an unclassified Pentagon email server that has caused the system to shut down for nearly two weeks was carried out by Russian hackers, NBC and The Daily Beast reported Thursday.
According to the reports, a "sophisticated cyber intrusion" on the Joint Chiefs of Staff's unclassified email system last month impacted 4,000 personnel. The Joint Chiefs' classified system was reportedly not affected.
NBC reports:
Sources tell NBC News that it appears the cyberattack relied on some kind of automated system that rapidly gathered massive amounts of data and within a minute distributed all the information to thousands of accounts on the Internet. The officials also report the suspected Russian hackers coordinated the sophisticated cyberassault via encrypted accounts on social media.
While the officials say its not clear whether the attack was sanctioned by the Russian government or conducted by individuals given the scope of the attack, "It was clearly the work of a state actor."
The email system was taken offline the weekend of July 25, and is expected to be restored soon.
Investigators reportedly believe the attack was carried out by the same hackers who breached the White House and the State Department last year. In that incident, investigators said hackers were able to breach the White House's unclassified system by first gaining access to the State Department's servers. The hackers are then believed to have sent a phishing email from a State Department account to access White House servers. Hackers were reportedly then able to access nonpublic details about President Barack Obama's schedule.
The Daily Beast reported earlier this month that Russian hackers had targeted the Defense Department with a phishing campaign.